Why are loader arms tapered?

[rus_geek]

Here's my vague understanding, based on trying to do beam calculations for trailer frames. Looking at a VERY simplified loader design, the red graph represents the forces acting on the loader arm, while the blue line represents the stress. (Anyone with more engineering than my paper napkin doodles should feel free to correct my terminology). The most stress in the member is at the point the cylinder contacts the arm. This is the point where the most strength is required. To either side of that, the arm can be tapered, due to the lower stress levels.

In the example of running into immovable objects (hitting a rock while plowing snow, for example), additional forces in the horizontal plane come into play.

-rus-

 

[CCWKen]

Your "kenbota" turned out great. Alot of thought and time went into the grader blade. To do some serious cutting in granite or hard clay do you have to add weights front and back ?

Granite? Hard clay? LOL... That's not going to happen with this little thing. It weighs around 1100lbs. The battery is in back and rear tires are filled with water. The Eaton hydro-driven rear transaxle is cast iron too but it will still break the tires loose in a heavy push. I made a tiller to run off the front PTO that I used to break up the soil before leveling. I built it to maintain the clay/sand drive way. After a heavy rain, I usually had to go out and clean-up the driveway. As long as the dirt was still a little moist, the Kenbota did a good job of moving it around. Once dry, it's like concrete.

Shortly after completing it, I ran across a JD-420C with a dozer blade in great running shape and cheap. So the Kenbota is used for clean-up and dress work. It's gets duty moving things around and digging up cactus too. Both machines are pre-tractor aquisition so I'll be building a blade the tractor soon. (Ford 3910) Evan so, there's jobs for all three machines for the time being. You can never have too many tools.

 

[czechsonofagun]

Here's my vague understanding, based on trying to do beam calculations for trailer frames. Looking at a VERY simplified loader design, the red graph represents the forces acting on the loader arm, while the blue line represents the stress. (Anyone with more engineering than my paper napkin doodles should feel free to correct my terminology). The most stress in the member is at the point the cylinder contacts the arm. This is the point where the most strength is required. To either side of that, the arm can be tapered, due to the lower stress levels.

In the example of running into immovable objects (hitting a rock while plowing snow, for example), additional forces in the horizontal plane come into play.

-rus-

you got it, but I can't help you with terminology either, since my ME degree is from the Czech University

 

[Renze]

Here's my vague understanding, based on trying to do beam calculations for trailer frames. Looking at a VERY simplified loader design, the red graph represents the forces acting on the loader arm, while the blue line represents the stress. (Anyone with more engineering than my paper napkin doodles should feel free to correct my terminology). The most stress in the member is at the point the cylinder contacts the arm. This is the point where the most strength is required. To either side of that, the arm can be tapered, due to the lower stress levels.

In the example of running into immovable objects (hitting a rock while plowing snow, for example), additional forces in the horizontal plane come into play.

pretty nice graphic representation of what they called the D and the M line at school... No idea what the official name is in English though..
What some engineers tend to forget, is that not just the stress from bending acts on the fibers, but also the shear forces of the very same load that causes the bending...
Just think of an overhead rolling crane in a welding shop: the consoles on which the crane rails rest, which are welded to the vertical poles of the building, are maybe a foot long. They can easily take the bending, but the material tension caused by the vertical shear force is about as much as the tension caused by the bending moment....

Here's my vague understanding, based on trying to do beam calculations for trailer frames. Looking at a VERY simplified loader design.....

I used to be a trailer engineer, but work as a loader engineer for 2 weeks now... on a loader, there is a lot more variety in forces and vectors than on a trailer frame....

 

[joes_427_vette]

Anyone mention " steel Grade " ? I'm sure there is better steel used in some loader frames due to the thickness of the material. My TL270 looks like it is less than 3/16 at the bucket end. The curved formed surface no doubt also adds strength also.

 

[Renze]

Anyone mention " steel Grade " ? I'm sure there is better steel used in some loader frames due to the thickness of the material. My TL270 looks like it is less than 3/16 at the bucket end. The curved formed surface no doubt also adds strength also.

For farm frontloaders, Domex, Weldox and Naxtra are popular brands of alloy:
Domex and Weldox is from Swedish Steel AB Trademarks - ssab.com
and Naxtra is from a German mill.

Domex has a very fine granular structure, which makes it less prone to fatigue cracking. Thats why it is very popular for tower cranes, truck mounted cranes, and construction machinery. Domex 700 is 3.5 times as strong as standard S235

 

[blacksmith]

The tapered section on my tractor is made from 3" square tubing cut into two pieces removing a wedge section and welded again. I hope this helps.

 

[crashz]

Rus Geek,

What you just posted was a classic Shear ( the red line) & Moment (the blue line) Diagram , complete with free body diagram of a beam with a point load, assuming axial tension or compression in the beam is not considered.

Nice job!